Tactile actuator and control method therefor

ABSTRACT

According to one embodiment, a tactile actuator can comprise: a housing having an accommodation space therein; a cap covering at least a portion of the accommodation space; a vibration unit disposed inside the accommodation space; an elastic member for connecting the housing and the vibration unit such that the vibration unit can vibrate with respect to the housing; a coil for forming a magnetic field to drive the vibration unit; and a control unit for determining any one driving mode on the basis of collected driving information from among a plurality of preset driving modes and determining, according to the driving mode, the characteristic of a current to be applied to the coil.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/763,208, filed 26 Mar. 2018 entitled “TACTILE ACTUATOR AND CONTROLMETHOD THEREFOR”, which is a National Stage of PCT/KR2016/006548, filedJun. 21, 2016 and claims the benefit of Korean Application No.10-2016-0076452, filed Jun. 20, 2016 and Korean Application No.10-2016-0052751, filed Apr. 29, 2016, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

Embodiments relate to a tactile actuator and a control method therefor.

BACKGROUND

Formerly, information was exchanged between electronic devices andhumans mainly through visual or auditory transmission. Recently, haptictechnology is emerging as technology for transmitting more specific andrealistic information.

In general, haptic devices for haptic technology include an inertialactuator, a piezoelectric actuator, and an electro-active polymeractuator (EAP).

The inertial actuator includes an eccentric rotation motor (ERM) thatvibrates using an eccentric force generated by a weight body connectedto a magnetic circuit, and a linear resonant actuator (LRA) thatmaximizes an intensity of vibration using a resonant frequency generatedby a weight body connected to a magnetic circuit and an elastic spring.

The piezoelectric actuator is a device that is driven in a form of a baror a disk using an elastic body, around a piezoelectric device with ashape that instantaneously deforms by an electric field.

In relation to the piezoelectric actuator, among the existing hapticdevices, there were published Korean Patent Publication No. 10-1603957(entitled Piezoelectric Actuator, Piezoelectric Vibration Apparatus, andPortable Terminal), and Korean Patent Application Publication No.10-2011-0118584 (entitled Transparent Composite Piezoelectric CombinedTouch Sensor and Haptic Actuator).

The EAP is a device that is driven by providing repeated motions usingan electro-active polymer film attached to a mass body, on the mainprinciple that a shape thereof deforms by a functional group of apolymer backbone having a specific mechanism by external electric power.

Further, in addition to the above haptic devices, haptic devices usingshape-memory alloys, electrostatic forces, or ultrasonic waves are beingdeveloped.

The above existing haptic devices merely transmit simple vibration.Besides, the LRA may vibrate effectively only when using a resonantfrequency determined by the mass body and the spring. The piezoelectricactuator uses a fragile material and thus may not achieve a sufficientdurability life for an operator. Last, the EAP has an issue ofdurability against external oxidation, and requires a large amount ofvoltage for actual driving, and thus may be difficult to apply tovarious devices.

Furthermore, according to the paper (entitled Tactile Sensing—FromHumans to Humanoids) published in the world-wide journal, IEEETRANSACTIONS ON ROBOTICS of 2010, a frequency of a tactile senseacceptable to a human body ranges from 0.4 hertz (Hz) to 500 Hz.However, when the existing haptic technology is used, only vibrationwithin the range of 160 Hz to 210 Hz may be provided, and thus morediverse and complex information may not be transmitted effectively. Tosolve the above issue effectively, research on an apparatus foreffectively transmitting a tactile signal within various frequencyranges is needed.

The existing haptic devices may seem to solve the above issue bywidening a bandwidth of a driving frequency to provide vibrationefficiently. However, due to a structure that simultaneously providessound and vibration of above 160 Hz, the vibration may be provided incompany with noise.

In addition, there is no apparatus that may provide a tactile senseincluding vibration in a low frequency region below 160 Hz.

Thus, there is a need for developing an apparatus that may provide atactile sense in a region below 160 Hz, and provide a tactile sense invarious ranges, rather than simply a single frequency region.

SUMMARY Technical Goals

As contrived to solve all the issues of the existing technology, inaddition to market needs for a new tactile sense with the development ofhaptic technology, embodiments provide a tactile device for providing amore sensitive tactile sense for various situations, that is, a tactileactuator.

An aspect provides a tactile actuator having at least two driving modes(operation modes) to suggest different tactile senses in at least twodistinguishing frequency bands and a control method therefor.

In detail, the aspect provides a tactile actuator that has at least oneresonant frequency below 160 Hz through a combination of an elasticmember and a vibrator (mess body), provides vibration that is providedby the existing technology at a corresponding point, and simultaneouslyhas a driving section to suggest another tactile sense at a point below⅓ the resonant frequency.

Another aspect provides a tactile actuator that suggests differenttactile senses by an external magnetic force through electric signals ofdifferent waveforms, even at the same frequency.

Technical Solutions

According to an aspect, there is provided a tactile actuator including ahousing having an accommodation space therein, a cap configured to coverat least a portion of the accommodation space, a vibrator disposed inthe accommodation space, an elastic member configured to connect thehousing and the vibrator such that the vibrator vibrates with respect tothe housing, a coil configured to form a magnetic field to drive thevibrator, and a controller configured to determine one of a plurality ofpreset driving modes based on collected driving information, anddetermine a characteristic of a current to be applied to the coil basedon the determined driving mode.

A mass of the vibrator may be below 2 grams (g), an elasticitycoefficient of the elastic member may be below 2.021 newtons permillimeter (N/mm), and a resonant frequency of the tactile actuator maybe below 160 hertz (Hz).

The controller may be configured to determine a frequency of the currentto be a first set frequency when the driving mode is a first set mode,and determine the frequency of the current to be a second set frequencywhen the driving mode is a set mode other than the first set mode, thesecond set frequency being lower than the first set frequency.

The first set frequency may be a value below 160 Hz.

The second set frequency may be a value below ⅓ the resonant frequencyof the tactile actuator.

The controller may be configured to determine a waveform of the currentto be a square wave or a pulse wave when the driving mode is a secondset mode, and determine the waveform of the current to be a sine wavewhen the driving mode is a third set mode.

The driving mode may include a general vibration mode, a tapping mode,and a rolling mode.

The controller may be configured to determine a frequency of the currentto be a first set frequency when the driving mode is the generalvibration mode, determine the frequency of the current to be a secondset frequency when the driving mode is the tapping mode, the second setfrequency being lower than the first set frequency, and determine thefrequency of the current to be a third set frequency when the drivingmode is the rolling mode, the third set frequency being higher than thesecond set frequency and lower than the first set frequency.

The tactile actuator may further include an information providing deviceconfigured to provide information collected by the controller, and theinformation providing device may include at least one of a userinterface configured to receive an instruction of a user, a sensorconfigured to sense an external environment, a memory configured tostore data, and a communicator configured to receive information throughcommunication with another communication device.

According to an aspect, there is provided a control method for a tactileactuator, the control method including collecting driving information,determining one of a plurality of preset driving modes based on thecollected driving information, determining a frequency of a current tobe applied to the coil based on the determined driving mode, andapplying the current to the coil.

The control method may further include determining a waveform of thecurrent to be applied to the coil based on the determined driving mode.

The driving information may be an image or a sound to be played back ina device connected to the tactile actuator, and the determining of thedriving mode may include determining the driving mode in real time basedon whether the image or the sound includes a preset image pattern or apreset audio pattern.

Effects

According to embodiments, various tactile senses may be transmitted moresensitively.

According to embodiments, in a frequency range below 160 Hz, of afrequency range that may be sensed by a human body, tactile senses maybe provided more efficiently than the existing technology.

According to embodiments, through a single tactile device, at least twodifferent tactile senses may be provided within a frequency range below160 Hz.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an inside of a tactile actuator according to anembodiment.

FIG. 2 illustrates an elastic member according to an embodiment.

FIG. 3 illustrates an elastic member according to another embodiment.

FIG. 4 is a block diagram of a tactile actuator according to anembodiment.

FIG. 5 is a graph conceptually illustrating a driving region withrespect to a frequency, in a tactile actuator according to anembodiment.

FIG. 6 is a graph illustrating a relationship between an actuallymeasured frequency and an acceleration, in a tactile actuator accordingto an embodiment.

FIG. 7 is a graph illustrating a relationship between a measuredfrequency and an acceleration when a square wave current having a lowfrequency is applied, in a tactile actuator according to an embodiment.

FIG. 8 is a graph illustrating a relationship between a measuredfrequency and an acceleration when a sine wave current having a lowfrequency is applied, in a tactile actuator according to an embodiment.

FIG. 9 illustrates a control method for a tactile actuator according toan embodiment.

FIG. 10 illustrates an example of a tactile actuator operating in afirst set mode according to an embodiment.

FIG. 11 illustrates another example of a tactile actuator operating in asecond set mode according to an embodiment.

FIG. 12 is a graph illustrating a change in an acceleration with respectto a change in an intensity of a square wave input current of 5 hertz(Hz), in tactile actuators having different resonant frequencies.

FIG. 13 is a graph illustrating a change in an acceleration with respectto a change in a frequency of a square wave input current of 90milliamperes (mA), in tactile actuators having different resonantfrequencies.

FIG. 14 illustrates waveforms of a vibrator exhibited in response to achange in a square wave current input into a tactile actuator having aresonant frequency characteristic of 80 Hz.

FIG. 15 illustrates waveforms of a vibrator exhibited in response to achange in a square wave current input into a tactile actuator having aresonant frequency characteristic of 120 Hz.

FIG. 16 illustrates waveforms of a vibrator exhibited in response to achange in a square wave current input into a tactile actuator having aresonant frequency characteristic of 160 Hz.

FIG. 17 illustrates waveforms of a vibrator exhibited in response to achange in a square wave current input into a tactile actuator having aresonant frequency characteristic of 180 Hz.

FIG. 18 is a graph illustrating threshold frequencies of tapping andvibration when a square wave current is applied, in tactile actuatorshaving different resonant frequencies.

FIG. 19 illustrates waveforms of a vibrator exhibited in response to achange in a pulse wave current input into a tactile actuator having aresonant frequency characteristic of 80 Hz.

FIG. 20 illustrates waveforms of a vibrator exhibited in response to achange in a pulse wave current input into a tactile actuator having aresonant frequency characteristic of 120 Hz.

FIG. 21 illustrates waveforms of a vibrator exhibited in response to achange in a pulse wave current input into a tactile actuator having aresonant frequency characteristic of 160 Hz.

FIG. 22 illustrates waveforms of a vibrator exhibited in response to achange in a pulse wave current input into a tactile actuator having aresonant frequency characteristic of 180 Hz.

FIG. 23 is a graph illustrating threshold frequencies of tapping andvibration when a pulse wave current is applied, in tactile actuatorshaving different resonant frequencies.

FIG. 24 illustrates waveforms of a vibrator exhibited in response to achange in a sine wave current input into a tactile actuator having aresonant frequency characteristic of 80 Hz.

FIG. 25 illustrates waveforms of a vibrator exhibited in response to achange in a sine wave current input into a tactile actuator having aresonant frequency characteristic of 120 Hz.

FIG. 26 illustrates waveforms of a vibrator exhibited in response to achange in a sine wave current input into a tactile actuator having aresonant frequency characteristic of 160 Hz.

FIG. 27 illustrates waveforms of a vibrator exhibited in response to achange in a sine wave current input into a tactile actuator having aresonant frequency characteristic of 180 Hz.

FIG. 28 is a graph illustrating threshold frequencies of rolling andvibration when a sine wave current is applied, in tactile actuatorshaving different resonant frequencies.

FIG. 29 illustrates a control method for a tactile actuator according toanother embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present disclosure will be describedwith reference to the accompanying drawings. Regarding the referencenumerals assigned to the components in the drawings, it should be notedthat the same components will be designated by the same referencenumerals, wherever possible, even though they are shown in differentdrawings. Also, in the description of the embodiments, detaileddescription of well-known related structures or functions will beomitted when it is deemed that such description will cause ambiguousinterpretation of the present disclosure.

Also, in the description of the components, terms such as first, second,A, B, (a), (b) or the like may be used herein when describing componentsof the present disclosure. Each of these terms is not used to define anessence, order or sequence of a corresponding component but used merelyto distinguish the corresponding component from other component(s). Itshould be noted that if it is described in the specification that onecomponent is “connected,” “coupled” or “joined” to another component,the former may be directly “connected,” “coupled,” and “joined” to thelatter or “connected”, “coupled”, and “joined” to the latter via anothercomponent.

The same name may be used to describe a component included in anembodiment and a component having a common function in anotherembodiment. Unless otherwise mentioned, the description on theembodiment may be applicable to the other embodiment and thus,duplicated description will be omitted for conciseness.

FIG. 1 illustrates an inside of a tactile actuator according to anembodiment, FIG. 2 illustrates an elastic member according to anembodiment, FIG. 3 illustrates an elastic member according to anotherembodiment, and FIG. 4 is a block diagram of the tactile actuatoraccording to an embodiment.

Referring to FIGS. 1 through 4 , a tactile actuator 1 may include ahousing 11, a cap 12, a vibrator 13, an elastic member 14, a coil 15, auser interface 16, a sensor 17, a memory 18, a communicator 19, and acontroller 20.

The housing 11 may include, for example, an accommodation space with anopened top. Although the housing 11 is illustrated as a box shape, theshape of the housing 11 is not limited thereto.

The cap 12 may cover at least a portion of the accommodation space. Anedge portion of the cap 12 may be fixed to a side wall of the housing11. Through a body of a user in direct or indirect contact with the cap12, vibration generated by the vibrator 13 may be transmitted. Forexample, the cap 12 may include a more flexible material than thehousing 11, so as to properly transmit a tactile sense such asvibration, tapping, or rolling of the vibrator 13 to the user.

The vibrator 13 may be disposed in the accommodation space of thehousing 11, and may be driven by a magnetic field generated by a currentapplied to the coil 15. The vibrator 13 may include a material to bedriven by the magnetic field. The vibrator 13 may be construed as a“magnetic circuit and mass body”.

For example, the vibrator 13 may be made of soft magnetic materialshaving intrinsic coercivities below at least 1000 amperes/meter (A/m),among ferromagnetic materials, and include a material having a structuresuch as steel, powder, alloy, alloy powder, composites, or ananostructure including at least one of elements such as Fe, Ni, Si, Mn,and Zn. The overall configuration may not need to be made of a singlematerial.

In another example, the vibrator 13 may include a material purelyincluding Cu or W having a specific gravity over 8, among paramagneticmaterials, or a material having a structure such as alloy, alloy powder,composites, or a nanostructure including at least one of the softmagnetic elements such as Fe, Ni, Si, Mn, and Zn mentioned above.Similarly, the material and the structure of the magnetic circuit andmass body may not need to be uniform.

A portion of the vibrator 13 may include a material having a structuresuch as steel, powder, alloy, alloy powder, composites, or ananostructure including at least one of elements such as Fe, Co, Ni, Nd,Ni, B, and Zn as the ferromagnetic materials, and include a materialmagnetized such that the N pole and the S pole thereof may bedistinguished in a vertical direction of FIG. 1 .

The elastic member 14 may connect the housing 11 and the vibrator 13such that the vibrator 13 may vibrate with respect to the housing 11.For example, the elastic member 14 may include a low paramagnetic ordiamagnetic material, for example, stainless steel, plastic, or rubber,which has an elasticity that may deform by an external force and berestored to its original shape immediately when the external forcedisappears.

The elastic member 14 may include a fixture 14 a fixed to the housing11, a support 14 b configured to support the vibrator 13, and aconnector 14 c configured to connect the fixture 14 a and the support 14b. For example, a diameter of the fixture 14 a may be greater than adiameter of the support 14 b.

Meanwhile, although FIGS. 1 and 2 exemplarily illustrate a case in whichthe fixture 14 a and the support 14 b are ring-shaped, a support 24 b ofan elastic member 24 may include a plurality of segments, as shown inFIG. 3 , which may also apply to the fixture 14 a.

The coil 15 may form a magnetic field to drive the vibrator 13 using thecurrent applied thereto. For example, the coil 15 may include a planarcoil, a solenoid coil, or an electromagnetic coil having a coreincluding soft magnetic materials.

The user interface 16 may receive an instruction directly from the user.For example, the user interface 16 may be a keyboard, a mouse, or atouch panel. However, the type of the user interface 16 is not limitedthereto.

The sensor 17 may sense an external environment of the tactile actuator1. For example, the sensor 17 may sense temperature, humidity, pressure,or light intensity, convert the sensed information into an electricsignal, and transmit the electric signal to the controller 20. However,the type of the sensor 17 is not limited thereto.

The memory 18 may store data. For example, data such as an image, asound, a photograph, or a text may be stored in the memory 18. Datareceived from the user interface 16, the sensor 17, and/or thecommunicator 19 may also be stored in the memory 18. A plurality ofpreset driving modes may also be stored in the memory 18.

The communicator 19 may receive information through wired or wirelesscommunication with another communication device. For example, thecommunicator 19 may receive external data such as an image, a sound, aphotograph, or a text through the Internet, and transmit the externaldata to the controller 20.

The user interface 16, the sensor 17, the memory 18, and thecommunicator 19 may be collectively referred to as an “informationproviding device”. The information providing device may provide drivinginformation collected by the controller 20. An embodiment relates to atactile actuator that may operate in a plurality of driving modes basedon information provided from the information providing device to acontroller. However, the type of the collected information or the typeof the device providing the information is not limited thereto.

The controller 20 may determine one of the plurality of preset drivingmodes based on the collected driving information. Here, the drivinginformation collected by the controller 20 may be information receivedfrom the information providing device. The controller 20 may determine acharacteristic of a current to be applied to the coil 15 based on thedetermined driving mode. Here, the characteristic of the current mayinclude a voltage, a frequency, and a waveform.

An embodiment may enable vibration in a low frequency region by changinga physical property of the elastic member 14. Table 1 showing anelasticity coefficient of an elastic member induced from a mass of avibrator and a resonant frequency of an existing tactile actuator basedon the following Equation 1, and Table 2 showing an elasticitycoefficient of the elastic member 14 of the tactile actuator 1 aresuggested as follows.

$\begin{matrix}{f = {\frac{1}{2\pi}\sqrt{\frac{k}{m}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

TABLE 1 Elasticity Coefficients of Elastic Members Used for ExistingTactile Actuator Spring Measured Freq. Mass Induced Spring Constant No.(Hz) (g) (N/mm) 1 154.7 1.578 1.491 2 154.1 1.578 1.479 3 152.7 1.5781.453 4 149.8 1.578 1.398 5 153.0 2.23 2.061 6 160.0 2.23 2.254

TABLE 2 Elasticity Coefficients of Elastic Members Used for TactileActuator According to Embodiment Spring Measured Freq. Mass InducedSpring Constant No. (Hz) (g) (N/mm) 7 98.7 0.65 0.250 8 81.4 0.79 0.2079 75.7 0.93 0.210 10 85.3 1.09 0.313 11 78.2 1.04 0.251

Referring to Table 1 and Table 2, the elasticity coefficient of theelastic member 14 may be set to be over 0.2 newtons per millimeter(N/mm) and below 0.35 N/mm such that a tactile actuator including, forexample, the vibrator 13 with a mess ranging from 0.6 to 1.1 grams (g)may have a low resonant frequency below 100 Hz.

FIG. 5 is a graph conceptually illustrating a driving region withrespect to a frequency, in a tactile actuator according to anembodiment, and FIG. 6 is a graph illustrating a relationship between anactually measured frequency and an acceleration, in the tactile actuatoraccording to an embodiment.

A solid line is a graph illustrating an operation of the tactileactuator 1, a dot-and-dash line is a graph illustrating an operation ofan existing general linear resonant actuator (LRA), and a broken line isa graph illustrating an operation of a multifunction vibration actuatorwith an improved driving frequency band from the existing general LRA.

Referring to FIGS. 5 and 6 , the tactile actuator 1 may have at leasttwo driving modes based on the current applied to the coil 15.

Referring to the graph (dot-and-dash line) of the existing general LRA,the existing general LRA has a maximum vibration force at a singleresonant frequency f_c above 170 Hz, and has a drivable frequency bandin a relatively narrow frequency band A3.

Since existing tactile methods are limited to vibration, outputs in afrequency band in which periodic vibration is not formed were defined asnoise and ignored, and thus the tactile methods failed to providevarious tactile senses.

Meanwhile, referring to the graph (solid line) of the tactile actuator,the tactile actuator has at least one resonant frequency f_a1 below 160Hz, and may suggest a tactile sense in a form of vibration that isoutput from an existing haptic device in a frequency band A11 includingthe corresponding resonant frequency f_a1.

Further, in a region below a threshold frequency f_a2 which isapproximately ⅓ the corresponding resonant frequency f_a1, the tactileactuator includes at least one different frequency band A12 in which aforce may be provided, rather than vibration, and the correspondingforce may be tactile senses such as tapping and rolling. Here, thethreshold frequency may be a minimum frequency at which periodicvibration is formed without showing collapse of a waveform generatedbased on an input current.

FIG. 7 is a graph illustrating a relationship between a measuredfrequency and an acceleration when a square wave current having a lowfrequency is applied, in a tactile actuator according to an embodiment,and FIG. 8 is a graph illustrating a relationship between a measuredfrequency and an acceleration when a sine wave current having a lowfrequency is applied, in the tactile actuator according to anembodiment.

A solid line is a graph illustrating an operation of the tactileactuator 1, and a dot-and-dash line is a graph illustrating an operationof the existing general LRA.

Referring to FIGS. 7 and 8 , when a current of a low frequency flows,the existing general LRA showed noise unsuitable for actual use, whereasthe tactile actuator 1 showed a vibration pattern suitable for awaveform of the provided external current.

FIG. 9 illustrates a control method for a tactile actuator according toan embodiment, FIG. 10 illustrates an example of an operation of thetactile actuator according to an embodiment, and FIG. 11 illustratesanother example of an operation of the tactile actuator according to anembodiment.

Referring to FIG. 9 through 11 , driving information input through theinformation providing device 16, 17, 18, 19 may be collected by thecontroller 20, in operation 100. Based on the driving informationcollected in operation 100, the controller 20 may determine one of aplurality of preset driving modes, in operation 110. Here, the pluralityof preset driving modes may include, for example, a general vibrationmode, a tapping mode, and/or a rolling mode. Hereinafter, a case inwhich a first set mode is the general vibration mode, a second set modeis the tapping mode, and a third set mode is the rolling mode will bedescribed.

For example, the driving information may be an image or a sound to beplayed back in a device connected to the tactile actuator 1. Inoperation 110, the driving mode may be determined in real time based onwhether the image or the sound to be played back includes a preset imagepattern or a preset audio pattern.

When the driving mode is determined in operation 110, the controller 20may determine a frequency of a current to be applied to the coil 15based on the determined driving mode.

Whether the driving mode determined in operation 110 is the generalvibration mode may be determined, in operation 120. When the determineddriving mode is the first set mode (general vibration mode), thecontroller 20 may determine the frequency of the current to be a firstset frequency f_H higher than a threshold frequency, which is a minimumfrequency to form a vibration force with a shape of a periodic sinewave, in operation 130. The controller 20 may apply the current of theset frequency to the coil 15, in operation 180. The first set frequencyf_H may be set to be a value belonging to the frequency band A11 of FIG.5 around the resonant frequency of the tactile actuator 1. For example,the first set frequency f_H may be a value below 160 Hz.

When the current having the first set frequency f_H is applied inoperation 180, the vibrator 13 may vibrate up and down in theaccommodation space of the housing 11, as shown in FIG. 10 . Thevibration may be transmitted to the user sequentially through theelastic member 14, the housing 11, and the cap 12. In the first setmode, a frequency high enough to form a periodic vibration force may beinput. Thus, similar vibration may be generated without being affectedgreatly by a type of an input waveform. That is, the type of the inputwaveform in the first set mode is not limited.

Meanwhile, when the driving mode determined in operation 110 is a setmode other than the first set mode, the controller 20 may determine thefrequency of the current to be the second set frequency f_L which islower than the first set frequency f_H, in operation 140. The second setfrequency f_L may be determined to be a value lower than the thresholdfrequency. For example, the second frequency f_L may be a value below ⅓the resonant frequency of the tactile actuator 1.

After operation 140 is performed, the controller 20 may determinewhether the driving mode is the second set mode (tapping mode), inoperation 150. When the driving mode is determined to be the second setmode (tapping mode) in operation 150, the controller 20 may determine awaveform of the current to be a square wave or a pulse wave. Conversely,when the driving mode is determined to be the third set mode (rollingmode) in operation 150, the controller 20 may determine the waveform ofthe current to be a sine wave. The controller 20 may apply the currentof the set frequency and the set waveform to the coil 15, in operation180.

When the current having the second set frequency f_L is applied inoperation 180, the vibrator 13 may not form a periodic vibration force,and thus transmit a different tactile sense to the user based on theinput waveform, as described below.

First, in a case in which the waveform of the input current is a sinewave, the vibrator 13 not forming a periodic vibration force may move upand down aperiodically. In addition, due to a characteristic of the sinewave, an intensity of the current input into the coil 15 may changegently. Thus, the user may feel a tactile sense of rolling through theabove motion. Herein, “rolling” may be construed as collectivelyreferring to a series of aperiodic tactile senses. When applying theabove conditions to a prototype in practice, the user felt a tactilesense of rolling.

Next, in a case in which the waveform of the input current is a squarewave or a pulse wave, the vibrator 13 not forming a periodic vibrationforce may similarly move up and down aperiodically. However, due to acharacteristic of the square wave or the pulse wave, the intensity ofthe current input into the coil 15 may change radically. Thus, at eachperiodic instant at which the intensity of the current changes, anacceleration in a direction in which the vibrator 13 moves up and downmay change much greatly, when compared to other sections. A tactilesense that the user feels at an instant at which the intensity of thecurrent changes may increase a threshold value of a sense of touch ofthe user, which may cause a sensory adaptation such that the user maynot feel a tactile sense in remaining sections. Thus, the user may feela tactile sense of “tapping”. Herein, “tapping” may be construed ascollectively referring to a tactile sense of periodically repeating animpulse high enough to be more distinguishing than the remainingsections. When applying the above conditions to a prototype in practice,the user felt a tactile sense of tapping.

That is, when a current having a frequency below ⅓ the resonantfrequency of the tactile actuator 1 is input, the user may feel at leasttwo different tactile senses based on a waveform of the current.

Meanwhile, for example, in a case in which a distance between thevibrator 13 and the cap 12 is sufficiently close, or a sufficientvoltage is input, the vibrator 13 may be in direct contact with the cap12, as shown in FIG. 11 , thereby transmitting a force directly to theuser through the cap 12.

Hereinafter, graphs showing experiment results using the tactileactuator 1 will be described in detail.

FIG. 12 is a graph illustrating a change in an acceleration with respectto a change in an intensity of a square wave input current of 5 hertz(Hz), in tactile actuators having different resonant frequencies, andFIG. 13 is a graph illustrating a change in an acceleration with respectto a change in a frequency of a square wave input current of 90milliamperes (mA), in the tactile actuators having different resonantfrequencies.

Through the experiments, it was learned that a user may feel a tactilesense of tapping when the vibrator 13 operates with an acceleration of0.2 G. Referring to FIGS. 12 and 13 , in a case in which the resonantfrequency of the tactile actuator 1 is below 160 Hz, the vibrator 13 mayoperate with an acceleration over 0.2 G although a current with anintensity of 90 mA and a frequency of 5 Hz is applied. Conversely, in acase in which the resonant frequency of the tactile actuator is 180 Hzwhich is a bit greater than 160 Hz, a current over 130 mA which is about1.5 times 90 mA may need to be applied such that the vibrator 13 mayoperate with an acceleration over 0.2 G.

In a case in which a mass of the vibrator 13 is below 2 g, the tactileactuator may set an elasticity coefficient of the elastic member 14 tobe below 2.021 N/mm, thereby setting the resonant frequency to be below160 Hz. Meanwhile, in a case in which the mass of the vibrator 13 isover 2 g, the tactile actuator may set the elasticity coefficient of theelastic member 14 to be over 2.021 N/mm, thereby setting the resonantfrequency to be below 160 Hz.

FIGS. 14 through 17 illustrate waveforms of vibrators exhibited inresponse to a change in a square wave current input into tactileactuators having resonant frequency characteristics of 80 Hz, 120 Hz,160 Hz, and 180 Hz, respectively, and FIG. 18 is a graph illustratingthreshold frequencies of tapping and vibration when a square wavecurrent is applied, in the tactile actuators having different resonantfrequencies.

Referring to FIGS. 14 through 17 , when a square wave current over apredetermined frequency is applied, a vibrator may form a vibrationforce of a shape of a sine wave which is a periodic waveform, as shownin the graphs in the right column of each drawing. Thus, under the aboveconditions, the tactile actuator may provide a tactile sense of“vibration” to the user.

Conversely, as shown in the graphs in the left column of each drawing,the vibrator may not form a periodic vibration force in a region belowthe predetermined frequency, and the graphs partially collapse. However,due to a characteristic of the square wave, at each periodic instance atwhich the intensity of the current changes, an acceleration of thevibrator may change much greatly, when compared to other sections. Thus,under the above conditions, the tactile actuator may provide a tactilesense of “tapping” to the user.

As described above, the tactile sense that the tactile actuator providesto the user may be divided as vibration or tapping based on thepredetermined frequency. The predetermined frequency may also bereferred to as a threshold frequency or a division frequency.

Referring to FIGS. 14 through 17 , as the resonant frequency of thetactile actuator increases, the threshold frequency may also increase,which is shown in FIG. 18 . In a control method for the tactileactuator, the first set frequency f_H and the second set frequency f_Lmay be set based on the threshold frequency of FIG. 18 .

FIGS. 19 through 22 illustrate waveforms of vibrators exhibited inresponse to a change in a pulse wave current input into tactileactuators having resonant frequency characteristics of 80 Hz, 120 Hz,160 Hz, and 180 Hz, respectively, and FIG. 23 is a graph illustratingthreshold frequencies of tapping and vibration when a pulse wave currentis applied, in the tactile actuators having different resonantfrequencies.

Referring to FIGS. 19 through 22 , when a pulse wave current is input, avibrator may have a similar waveform to a case in which a square wavecurrent is input. Thus, when a pulse wave current below a thresholdfrequency is applied to the tactile actuator, the tactile actuator mayprovide a tactile sense of “tapping” to the user. When a pulse wavecurrent over the threshold frequency is applied to the tactile actuator,the tactile actuator may provide a tactile sense of “vibration” to theuser.

Referring to FIGS. 19 through 22 , as the resonant frequency of thetactile actuator increases, the threshold frequency may also increase,which is shown in FIG. 23 .

Meanwhile, with respect to the tactile actuator having the same resonantfrequency, a threshold frequency when inputting a pulse wave current maybe about two times a threshold frequency when inputting a square wavecurrent.

In a control method for the tactile actuator, the first set frequencyf_H and the second set frequency f_L may be set based on the thresholdfrequency of FIG. 23 .

FIGS. 24 through 27 illustrate waveforms of vibrators exhibited inresponse to a change in a sine wave current input into tactile actuatorshaving resonant frequency characteristics of 80 Hz, 120 Hz, 160 Hz, and180 Hz, respectively, and FIG. 28 is a graph illustrating thresholdfrequencies of rolling and vibration when a sine wave current isapplied, in the tactile actuators having different resonant frequencies.

Referring to FIGS. 24 through 27 , when a sine wave current over apredetermined frequency is applied, a vibrator may form a vibrationforce of a shape of a sine wave which is a periodic waveform, as shownin the graphs in the right column of each drawing. Thus, under the aboveconditions, the tactile actuator may provide a tactile sense of“vibration” to the user.

Conversely, as shown in the graphs in the left column of each drawing,the vibrator may not form a periodic vibration force in a region belowthe predetermined frequency, and the graphs partially collapse. Thevibrator not forming a periodic vibration force may have an accelerationof a vertical motion aperiodically. Meanwhile, due to a characteristicof the sine wave, an intensity of the current may change gently, andthus the user may feel a tactile sense of “rolling” through the abovemotion.

As described above, the tactile sense that the tactile actuator providesto the user may be divided as vibration or rolling based on thepredetermined frequency.

Referring to FIGS. 24 through 27 , as the resonant frequency of thetactile actuator increases, the threshold frequency may also increase,which is shown in FIG. 28 . In a control method for the tactileactuator, the first set frequency f_H and the second set frequency f_Lmay be set based on the threshold frequency of FIG. 28 .

FIG. 29 illustrates a control method for a tactile actuator according toanother embodiment. Unless otherwise disclosed, the description of thecontrol method for the tactile actuator provided with reference to FIG.9 may also apply to the other embodiment.

Referring to FIG. 29 , in a control method for the tactile actuator,when a driving mode is a general vibration mode in operation 120, thecontroller may determine a frequency of a current to be applied to be afirst set frequency f_H. With reference to FIG. 18, 23 , or 28, thefirst set frequency f_H may be set to be a value greater than a firstthreshold frequency which is a minimum frequency to provide a tactilesense of “vibration” under provide conditions.

When the driving mode is not the general vibration mode in operation120, the controller may determine whether the driving mode is a tappingmode, in operation 150.

In a case in which the driving mode is the tapping mode in operation150, the controller may determine the frequency of the current to beapplied to be a second set frequency f_L1, in operation 151. Withreference to FIG. 18 or 23 , the second set frequency f_L1 may be set tobe a value less than a second threshold frequency which is a maximumfrequency to provide a tactile sense of “tapping” under providedconditions.

In a case in which the driving mode is not the tapping mode in operation150, the controller may determine the frequency of the current to beapplied to be a third set frequency f_L2, in operation 152. Withreference to FIG. 28 , the third set frequency f_L2 may be set to be avalue less than a third threshold frequency which is a maximum frequencyto provide a tactile sense of “rolling” under provided conditions.

Meanwhile, as shown in FIGS. 18, 23, and 28 , the third thresholdfrequency which is a maximum frequency to provide a tactile sense of“rolling” may be greater than the second threshold frequency which is amaximum frequency to provide a tactile sense of “tapping” under the sameconditions. Thus, the third set frequency f_L2 may be set to be higherthan the second set frequency f_L1. Meanwhile, the first set frequencyf_H may be set to be a value greater than the second set frequency f_L1and the third set frequency f_L2. That is, the third set frequency f_L2may be greater than the second set frequency f_L1, and the first setfrequency f_H may be greater than the third set frequency f_L2.

According to the above embodiments, various tactile senses may betransmitted more sensitively. Further, in a frequency range below 160Hz, of a frequency range that may be sensed by a human body, tactilesenses may be provided more efficiently than the existing technology. Inaddition, through a single tactile device, at least two differenttactile senses may be provided within a frequency range below 160 Hz.

Although a few embodiments of the present invention have been shown anddescribed, the present invention is not limited to the describedembodiments. Instead, it would be appreciated by those skilled in theart that changes may be made to these embodiments without departing fromthe principles and spirit of the invention, the scope of which isdefined by the claims and their equivalents.

The invention claimed is:
 1. A control method of a tactile actuator, thetactile actuator including a coil and driven by a magnetic fieldgenerated by a current applied to the coil, the control methodcomprising: determining any one driving mode from among a plurality ofpreset driving modes based on driving information; determining afrequency of a current to be applied to the coil based on the determineddriving mode; and applying a current to the coil, wherein the drivingmode includes: a first mode driven at a resonant frequency of thetactile actuator, and a second mode driven at or below a thresholdfrequency of the tactile actuator, and wherein the threshold frequencyis a minimum frequency that forms a periodic vibration without showingcollapse of a waveform generated based on the applied current.
 2. Thecontrol method of claim 1, wherein a resonant frequency of the tactileactuator is 160 hertz (Hz) or less.
 3. The control method of claim 1,wherein the threshold frequency of the tactile actuator is a value of ⅓or less of the resonant frequency of the tactile actuator.
 4. Thecontrol method of claim 1, wherein the driving information is an imageor a sound to be played back in a device connected to the tactileactuator, and the determining of the driving mode comprises determiningthe driving mode in real time based on whether the image or the soundincludes a preset pattern.
 5. The control method of claim 1, wherein thefirst mode is a mode that provides vibration, and wherein the secondmode is a mode that provides tapping or rolling.
 6. The control methodof claim 5, wherein the tapping or rolling is provided when the waveformof the applied current is at least one of a square wave, a pulse wave,and a sine wave.
 7. The control method of claim 6, wherein the waveformof the applied current is a square wave or a pulse wave when the drivingmode is the mode that provides rolling, and wherein the waveform of theapplied current is a sine wave when the driving mode is the mode thatprovides tapping.
 8. The control method of claim 5, wherein thefrequency of the current for providing the tapping is lower than thefrequency of the current for providing the rolling.
 9. The controlmethod of claim 1, wherein the tactile actuator comprises: a housinghaving an accommodation space therein; a cap configured to cover atleast a portion of the accommodation space; a vibrator disposed in theaccommodation space; an elastic member configured to connect the housingand the vibrator such that the vibrator vibrates with respect to thehousing; and the coil configured to form the magnetic field to drive thevibrator.
 10. The control method of claim 9, wherein, when the mass ofthe vibrator is 2 grams or less, the elasticity coefficient of theelastic member is set to be 2.021 N/mm or less so that the resonantfrequency of the tactile actuator is 160 Hz or less, and wherein, whenthe mass of the vibrator is 2 grams or more, the elasticity coefficientof the elastic member is set to be 2.021 N/mm or more so that theresonant frequency of the tactile actuator is 160 Hz or less.
 11. Acontrol method of a device, the device configured to provide tactilesensation using a tactile actuator, the tactile actuator including acoil and driven by a magnetic field generated by a current applied tothe coil, the control method comprising: determining any one drivingmode from among a plurality of preset driving modes based on drivinginformation; determining a frequency of a current to be applied to thecoil based on the determined driving mode; and applying a current to thecoil, wherein the driving mode includes: a first mode driven at aresonant frequency of the tactile actuator, and a second mode driven ator below a threshold frequency of the tactile actuator, and wherein thethreshold frequency is a minimum frequency that forms a periodicvibration without showing collapse of a waveform generated based on theapplied current.